1. Field of Invention
The present invention relates to image display apparatuses. In particular, the present invention relates to an image display apparatus that captures surrounding images of a vehicle by using multiple cameras, combines the captured images to draw, in a frame memory, a composite image viewed from a viewpoint above the vehicle, reads image data from the frame memory, and displays the composite image.
2. Description of the Related Art
Systems for assisting drivers in putting vehicles into garages or parking the vehicles are under research and are also in practical use. With such an assisting system, a top-view system is known (refer to Japanese Patent No. 3300334). In the system, surrounding images of a vehicle are captured using multiple cameras, the captured images are combined to draw, in a frame memory, a composite image (a top-view image) viewed from a viewpoint above the vehicle, and image data is read from the frame memory to display the composite image.
In the top-view system, as shown in FIGS. 21A and 21B, fisheye cameras 1a to 1d for photographing the surroundings of a vehicle 2 are attached to a front portion, a left-side portion, a right-side portion, and a rear portion thereof. A composite-image processor 3 uses images captured by the cameras 1a to 1d to create a composite image of a landscape viewed in a predetermined direction from a predetermined position (a virtual viewpoint) 4 above the vehicle 2, as shown in FIG. 21C, and the composite image is displayed on a monitor 5, thereby assisting the driver, for example, in parking the vehicle and putting the vehicle into the garage.
During the combining processing, the composite-image processor 3 uses a mapping table to map image portions photographed by the cameras to a frame memory, and displays the mapped image. FIG. 22 is a diagram illustrating a case in which fisheye graphics IMa to IMd photographed by the fisheye cameras 1a to 1d are mapped to a screen frame memory 6. The fisheye graphics IMa to IMd are mapped to corresponding areas 6a to 6d in the frame memory 6, and a vehicle image 7 pre-photographed and stored is mapped to a center portion of the frame memory 6. Consequently, a top-view image for one screen is generated in the frame memory 6.
FIG. 23 is a detailed diagram illustrating the mapping method. The fisheye cameras 1a to 1d attached to the vehicle 2 photograph a landscape ahead of the vehicle, a landscape at the left side of the vehicle, a landscape at the right side of the vehicle, and a landscape behind the vehicle, respectively. Using a fisheye lens, each of the cameras 1a to 1d can photograph a landscape in the range of 185° in front of the camera. The camera 1a photographs a landscape ahead of line FF, the camera 1b photographs a vehicle-left-side landscape at the left side of line LL, the camera 1c photographs a vehicle-right-side landscape at the right side of line RR, and the camera 1d photographs a vehicle rear landscape behind line BB.
When a rectangular grid pattern drawn on the ground at the left side of the vehicle 2 is photographed by the camera 1b, as shown in FIG. 23B, a graphics viewed by a fisheye (the graphics is herein referred to as a “fisheye graphics”) is obtained as shown in FIG. 23C.
Projecting the fisheye graphics photographed by the cameras 1a to 1d can provide a top-view image. In a rectangular graphics 6 and a fisheye graphics 7, areas denoted by the same reference numerals correspond to each other. That is, areas 1 to 6 in the rectangular graphics 6 correspond to areas 1 to 6 in the fisheye graphics 7. Thus, when images of the areas 1 to 6 in the fisheye graphics 7 which correspond to images of the areas 1 to 6 in the rectangular graphics 6 are stored at frame-memory positions where the images of the areas 1 to 6 in the rectangular graphics are to be stored, and similarly, images photographed by all the cameras are drawn in the frame memory and are read. Thus, the images photographed by the fisheye cameras 1a to 1d are view-converted into a graphics projected on a ground plane.
As described above, conventionally, images of the multiple cameras are projected onto a plain ground to generate a top-view image. However, when the vehicle body is tilted relative to the ground by passengers, the camera positions change and the positional relationship between the cameras and the projection plain is displaced. As a result, there is a problem in that connections of images photographed by the multiple cameras are displaced in the top-view image. FIGS. 24A and 24B illustrate such a problem. FIG. 24A shows a case in which the vehicle body is not titled and FIG. 24B shows a case in which the vehicle body is tilted by θ as a result of an increase in the number of passengers in the back seats. In the case of FIG. 24B, the position of the camera 1d comes down. Consequently, when the vehicle body is not tilted, no displacement occurs at connections CN of the images IMb to IMc photographed by the cameras 1b and 1c and the image IMd, as shown in FIG. 25A. When the vehicle body is tilted, vertical lines at the image connections CN are displaced, as show in FIG. 25B. FIG. 25A shows a top-view image when a total of two people are in the driver's seat and the front passenger seat, and FIG. 25B shows a top-view image when a total of seven people including the two people in the driver's seat and the front passenger seat and five people in the back seats. When two people are riding in the vehicle, the connections of floor lines substantially match each other, but when seven people are riding in the vehicle, the load of the rear side of the vehicle increases to lower the camera positions, so that the positional relationships between the cameras and the projection plain are displaced. As a result, vertical lines on the floor do not connect with each other.
Japanese Unexamined Patent Application Publication No. 2002-324235 discloses a technology that makes it easy to view a screen when a composite image resulting from images photographed by multiple vehicle-mounted cameras is displayed. In the known technology, multiple cameras for photographing the surroundings of a vehicle are attached to the vehicle, and images photographed by the cameras are combined and displayed on a screen of a display apparatus. During the display, pixel data of the images are corrected so that a difference between pixel data of the adjacent images is reduced. For example, the pixel data are corrected so that averages of pixel data of the adjacent images become equal to each other, thereby making the composite image easy to view.
The known technologies described above, however, do not prevent displacement at a connection of camera images which is caused by tilt of the vehicle body from occurring in a top view image.